The present invention relates to an apparatus and method for friction welding. Specifically, the present invention relates to an apparatus and method for friction welding that produces an arcuate oscillating motion.
In general terms, a gas turbine engine has a compressor section, a combustion section and a turbine section. Air travels axially through the engine within an annular flow path. First, the air enters the compressor section. The compressor section pressurizes the air. The air then travels to the combustion section. The combustion section introduces fuel to the air and ignites the mixture. The air then travels to the turbine section. The turbine section extracts energy from the exhaust to drive the compressor. The air then exits the engine as thrust.
The compressor and turbine sections each include one or more bladed rotor assemblies. A rotor assembly includes a disk/rotor and a plurality of blades secured the outer diameter of the disk. Several techniques exist to secure the blades to the disk.
One such technique uses complementary shaped retention features on the disk and the blades. Specifically, the disk includes an arrangement of slots, each receiving a dovetail or fir tree arrangement on the root of the blade. This technique can have issues with manufacturing (e.g. the machining of complex slots in the disk) and weight.
Another technique involves the bonding or welding of the blades to the disk. Bonding the blades to the disk produces an integrally bladed rotor (IBR) assembly. This technique is preferred when considering possible weight savings. A rotor assembly using the aforementioned slot/dovetail arrangement will weigh more than an IBR since the IBR does not require blade platforms or roots.
One method of producing an IBR is friction welding. Friction welding utilizes complementary interfacing surfaces of the blade and the disk. The friction welding machine rubs the interfacing surfaces of the blade and the disk together in an oscillating pattern. The friction created at the interface generates heat. The heat produces a molten, preferably plastic, state to the material at the interfacing surfaces.
As the parts rub, the machine applies a compressive force to increase pressure at the interface. This forge load causes some of the molten material to exit the interface. This flash flow of molten material from the interface by the forge load causes a gradual decrease in part thickness (in the forge direction, i.e. perpendicular to the interface).
At a desired thickness, the machine terminates the rubbing of the blade and disk. As a result, flash flow will cease. In addition, the interfacing surfaces of the blade and the disk will cool. Upon cooling, the interface reverts to a solid structure. The parts together are now joined together as one piece.
Conventional friction welding machines utilize a linear oscillating motion when rubbing the blade and the disk together. Most conventional linear friction welding machines hold the blade with the airfoil chord aligned with the axis of oscillation. The phrase xe2x80x9cairfoil chordxe2x80x9d refers the straight line between the ends of the mean camber line of an airfoil. The phrase xe2x80x9cmean camber linexe2x80x9d refers the locus of points equidistant from the upper and lower surfaces of an airfoil.
This alignment has proven successful for blades with low camber. The term xe2x80x9ccamberxe2x80x9d refers to the distance between the airfoil chord and the mean camber line.
A common problem encountered by conventional linear friction welding machines is notch effect. As the blade moves in relation to the disk, an overhang occurs at either end of the oscillation path. The overhang has more direct exposure to the atmosphere than the remainder of the interface between the parts. As a result, the overhang is cooler than the remainder of the interface. In fact, the bond interface at the overhang prematurely cools, causing notches.
The solution to the aforementioned notch effect is to provide extra material or sacrificial tips to the blade.
As the camber of the airfoil deepens, however, overhang also occurs along the sides of the blade where the edges of the two parts are not parallel to the linear axis of oscillation. An airfoil with xe2x80x9cdeepxe2x80x9d camber has leading and trailing edges extending at an angle to the camber line greater than a low, or shallow, camber airfoil.
The use of the aforementioned sacrificial material along the sides of the blade is not practical with deep camber airfoils. The present invention, however, provides an effective solution.
It is an object of the present invention to provide an improved friction welding method and apparatus.
It is a further object of the present invention to provide a friction welding method and apparatus compatible with curved workpieces.
It is a further object of the present invention to provide a friction welding method and apparatus compatible with blades having camber.
It is a further object of the present invention to provide a friction welding method and apparatus compatible with blades having deep camber.
It is a further object of the present invention to provide a friction welding method and apparatus that oscillates in a path that better conforms to the mean camber line of the airfoil section of the blade.
It is a further object of the present invention to provide a friction welding method and apparatus that provides uniform flash flow.
It is a further object of the present invention to provide a friction welding method and apparatus that reduces notch effect.
It is a further object of the present invention to provide a friction welding method and apparatus that exhibits reduced machine loading.
These and other objects of the present invention are achieved in one aspect by an apparatus for friction welding a workpiece to a substrate, comprising: an actuator producing a linear oscillating motion; a platform for supporting the workpiece; and a slide mechanism between the actuator and the platform. The slide mechanism converts the linear oscillating motion of the actuator into an arcuate oscillating motion of the platform so the platform can move the workpiece in the arcuate oscillating motion against the substrate.
These and other objects of the present invention are achieved in another aspect by a slide mechanism for a friction welding apparatus having an actuator and a platform for supporting a workpiece. The slide mechanism comprises: a base; and a guide engaging the platform and converting a linear oscillating motion of the actuator into an arcuate oscillating motion of the platform.
These and other objects of the present invention are achieved in another aspect by a method of friction welding a curved workpiece, having a leading edge and a trailing edge, to a substrate. The method comprises the steps of: providing an actuator which generates a linear oscillating motion; converting the linear oscillating motion of the actuator into an arcuate oscillating motion of the workpiece; and contacting the substrate with the workpiece with a force sufficient to bond the workpiece to the substrate.